The overall purpose of this project is to produce radiolabeled tumor-localizing antibodies useful in the diagnosis, anatomical localization, and management of feline lymphomas. The specified aims are: (1)\to produce monoclonal antibodies to feline leukemia virus (FeLV) antigens and feline oncovirus-associated cell membrane antigen (FOCMA); (2)\to develop methods of producing 131I, 123I, and 111In-labeled FeLV and FOCMA monoclonal antibody preparations; (3)\to test the bind-ing of radiolabeled FeLV and FOCMA monoclonal antibodies to FeLV-induced FL-74 cells in vitro; (4)\to evaluate the utility of radiolabeled FeLV or FOCMA monoclonal antibodies for the in vivo localization of tumor in cats with spontaneous lymphoma; and (5)\to develop and test an immunodiagnostic ELISA assay for FeLV infection utilizing monoclonal antibody to FeLV p15E antigen. Various diseases in cats are caused by FeLV. FeLV is transmitted horizontally from cat to cat through saliva by licking or biting. About 30% of FeLV-exposed cats do not develop significant immune resistance and become persistently infected with FeLV. About 83% of FeLV-infected healthy cats will die within 3 years of infection. Lymphosarcoma occurs annually in about 200 cats per 100,000 cats in the population. It is estimated there are about 27 million cats in the United States. The tumor localization and biodistribution of the radiolabeled antibody preparations will be studied in spontaneous cases of lymphoma using tissue sampling and external scintigraphy. The parameters to be investigated are the antibody, radiolabel, dose, time after administration, the use of whole antibody or antibody fragments, and tumor size. The kinetics of antibody localization and conditions for optimizing image resolution by external scintigraphic imaging will be evaluated. The plan is to enter 15 to 20 patients per year. Imaging with radiolabeled monoclonal antibodies could be useful in the overall staging of newly diagnosed patients by delineating sites not seen with standard procedures. Irradiation may be curative in any localized lymphoma. The knowledge of the actual extent of disease would be critical to determine areas to be treated. A sensitive and specific technique for detecting small quantities of tumor would greatly facilitate patient monitoring in all phases of management. (2)